The present invention relates to mixing fuel and combustion air in preparation for burning the mixture in an internal combustion engine.
Most modern four cycle engines in automobiles use an individual injector to meter fuel into combustion air for each cylinder. Each injector is placed to one side of its air duct and tilted to aim its spray at the intake valve for its cylinder. A fine spray of fuel from the injector starts at a point on the wall of a combustion air duct, mixes with combustion air and then moves through an intake valve and into the cylinder during the intake stroke for the cylinder. Refer to FIG. 1. During this period and while passing through the intake valve, the fuel must vaporize and mix with the air so that a combustible mixture is ready for ignition. Although the fuel is highly volatile, achieving a perfect stoichiometric mixture throughout the cylinder is difficult because of the short time allowed. A six-cylinder engine at 3000 rpm has approximately 0.03 seconds to accomplish mixing, vaporization, move the air-fuel mixture into the cylinder and compress the mixture before ignition. Some engines inject fuel only during the intake cycle (sequential injection). Other engines inject fuel each revolution, on the intake stroke and also when the intake valve is closed (simultaneous port injection).
Perfect mixing of fuel and combustion air is approached, but never achieved, on the macroscopic level. There are small “pockets” of gas in the cylinder where fuel concentration is above (rich) or below (lean) the ideal concentration for stoichiometric combustion. Rich pockets with a shortage of oxygen burn cool and result in incompletely burned carbon and uneconomical loss of energy. Lean pockets with an excess of oxygen burn at high temperature. At high temperatures inert N2 molecules dissociate into highly reactive N atoms which then combine with oxygen to form a range of several oxygen-nitrogen compounds commonly referred to as NOx. NOx is an undesirable air pollutant, and thought to take part in smog formation. While burned exhaust gas is often re-injected into the engine to complete combustion; this method can result in lower efficiency for the engine. Also, a catalytic converter is used to further combustion.